USCIS posts specifics on how to file, were, and what is expected. the process is time consuming and other forms may need to be filed to gain EAD. your file has a quota - they provide the outcome then all others need to wait in the que for the following year quotas. https://www.uscis.gov/I-918

I filed mine in Dec 2018. I have not received anything yet. they are working on late 2016 and early 2017 new.

i received today work authorization filed in 2017